Advancements in Upper Body Exoskeleton: Implementing Active Gravity Compensation with a Feedforward Controller

TL;DR

This paper introduces a feedforward control system for an upper body exoskeleton that uses internal sensors and Newton-Euler equations to achieve active gravity compensation, reducing hardware complexity and improving response.

Contribution

It presents a novel feedforward control approach for exoskeletons that eliminates external torque sensors and enhances stability and performance.

Findings

Stable performance demonstrated on hardware and simulations

Reduced hardware complexity and weight

Proactive response with minimal friction

Abstract

In this study, we present a feedforward control system designed for active gravity compensation on an upper body exoskeleton. The system utilizes only positional data from internal motor sensors to calculate torque, employing analytical control equations based on Newton-Euler Inverse Dynamics. Compared to feedback control systems, the feedforward approach offers several advantages. It eliminates the need for external torque sensors, resulting in reduced hardware complexity and weight. Moreover, the feedforward control exhibits a more proactive response, leading to enhanced performance. The exoskeleton used in the experiments is lightweight and comprises 4 Degrees of Freedom, closely mimicking human upper body kinematics and three-dimensional range of motion. We conducted tests on both hardware and simulations of the exoskeleton, demonstrating stable performance. The system maintained its position over an extended period, exhibiting minimal friction and avoiding undesired slewing.